Definitions of plant and light science terms for growing indoors under lights

Definitions of plant and light science terms for growing indoors under lights

My new book on Growing Plants Under Lights will be released in spring 2018. To accompany the book, here is a Glossary of Terms related to plant and light science that you'll use when growing indoors under lights. Use these terms to help you better understand processes such as photosynthesis, photoperiodism, plant growth, propagation, and light science.

Auto-flowering. Entering the flowering stage based on plant age rather than season or daylength.

Auxins. Plant hormones found in shoots and roots

Ballast. A resister that limits the electrical current to a light bulb (lamp).

Biochrome. Biological pigment in plants.

Bolting. The process by which rosette plants elongate their stems. It occurs when flowering is induced in long-day plants or cold-requiring plants. However, bolting is not the same as flowering. Sometimes, the stem would elongate but flower buds would not be formed. However, the term is often used synonymously with flowering.

Cold-requiring plants. The plants which are induced to flower when exposed to low temperatures.

Come true. Seeds of a given plant species or variety will produce the same variety as the parent plant. Seeds of open-pollinated plants come true.

Cotyledon-seed coat. A hard seed coat which requires swelling.

Critical dark period. (critical nightlength, critical night) The length of night or dark period in a 24-hour cycle required to induce flowering of short-day plants, or inhibit flowering of long-day plants. When the length of night is longer than the critical dark period, short-day plants are induced to flower and long-day plants do not flower. In a natural setting, critical dark period is 24 hours minus critical daylength. Since the factor regulating photoperiodic flowering is not daylength but nightlength, the critical dark period rather than critical daylength should be referred to. “Nightlength” is also spelled “night length”.

Critical day. The same as “critical daylength”.

Critical daylength (critical day, critical photoperiod). The length of daylight within a 24-hour cycle (balanced with critical dark period) required to induce flowering of long-day plants or to inhibit flowering of short-day plants. When the daylength is longer than the critical daylength, long-day plants are induced to flower and short-day plants do not flower.

Critical night. The same as “critical dark period”.

Critical nightlength. The same as “critical dark period”.

Critical photoperiod. The same as “critical daylength”.

Cryptochromes. Blue light photoreceptors.

Cultivar. A plant variety resulting from an intentional hybridization of two related plants, or intentional selection of a naturally occurring variety, for cultivation in the marketplace. Seeds from cultivars to not come true, but cultivars may be replicated via vegetative cuttings or division.

Cytokinins. Phytohormones that promote lateral growth

Daylength. The same as “photoperiod”. Also spelled “day length”.

Day-neutral plants. The plants whose flowering does not depend on night length. The flowering of day-neutral plants is triggered when plants reach a certain age.

Deciduous. Plants that lose their leaves when the season changes.

Devernalization. The reversal of the effect of an inductive cold temperature in vernalization by exposure to warm temperatures.

DIF. The numeric value between daytime and nighttime temperatures, which you calculate by subtracting the nighttime temperature from the daytime temperature.

DLI Daily Light Integral. Total quantity of light delivered over an entire day, with the time period measured in hours.

Dormancy. Temporary inactivity at a metabolic level.

Facultative long-day plants (quantitative long-day plants). The plants whose flowering is promoted by a long-day (short-night) photoperiod. They can flower even under alternate photoperiods, although flowering is delayed. Antonym is “absolute long-day plants”.

Facultative response (quantitative response). The response which is promoted by a suitable photoperiod. The response could occur even under an inappropriate condition, although it is delayed. Antonym is “absolute response”.

Facultative short-day plants (quantitative short-day plants). The plants whose flowering is promoted by a short-day (long-night) photoperiod. They can flower even under inappropriate photoperiods, although flowering is delayed. Antonym is “absolute short-day plants”.

Fermenting. Process that converts sugar to acids, gases, or alcohol. Process used to prepare wet seeds.

Hybrid. A cross-breed of two plants that is not necessarily reproducible

Hydrophilic. Water absorbent.

Hydroponic. Growing plants in water.

Incandescent. Lamp type that creates light by heating a filament.

Indole butyric acid (IBA). A hormone used to produce clones via cuttings and for rooting

Infrared. Light with a longer wavelength than the visible spectrum---felt as heat.

Intermediate-day plants. The plants which flower when the dark length is between certain durations. An example is Salsola komarovii, which flowers when nightlength is around 12 hours. Flowering is delayed under both longer and shorter nightlengths. This type of plant is quite rare. The intermediate-day plant is a modification of a short-day plant.

Vernalization. The initiation of a flower by exposure to a specific period of low temperature (0 to 5 ℃). Also the promotive effects of low temperatures on flowering. Sometimes spelled “vernalisation”.

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